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Condensation Inside Bath Exhaust Fan Ducts?!? Help!

8 years ago

Hello. I've searched, but did not see any topic discussing how to fix this issue, or any preventive measures. Thanks in advance for your advice. I cannot figure how millions of homes are built, yet three homes in our neighborhood seem to have this problem.

At least three homes in this small 12 home neighborhood have the same issue. We had the same builder. Our floorplan is very different - the other two homes have very similar floorplans to each other I'll address our issue.

Home is located northern mid-atlantic, just east of the mountain foothills, maybe 1.5 hours west of the coast. Home is custom, built between March and September 2011. We've been moved in just over 3 years.
We opted to upgrade the insulation during construction, and got the new blown insulation (which we LOVE, btw). My husband says it's "blown in rockwood or fiberglass over spray-in closed cell". This is for all above-ground square footage.
Home has a main-level master.

The issue is with at least two bathroom exhaust fans. The fans vent through the roof. I don't think the exhaust fan ducting is insulated - it only goes up from the insulated space, through the colder attic barrier, then through the roof.
So ONLY during cold weather, we get condensation which forms on the INSIDE of the fan duct. This is causing ceiling drywall water damage where the exhaust fan cover meets the drywall, covering the fan blades.
During this last cold spell, temps got down to 5 to 15 degrees for several days. When we ran the bathroom fans, after we turned the fan off, we saw water. From one fan, the water would almost pour - drip very fast & quickly - directly from the fan vent, splashing onto the floor. That one wasn't so bad.
The MBR bath exhaust fan must have a different angle or some aspect of the flashing which allows the exhaust condensation to completely SOAK the surrounding ceiling drywall on that side of the fan. My husband took the fan cover off, and pushed up on the drywall - reminded me of rolled play-dough. There also were blisters of water, which when popped, the water splashed onto the floor tiles. It's bad.

One of our neighbors had his ducts "wrapped" trying to fix. Now we don't yet know WHAT the ducts were wrapped with, but he said this did not work. (our run isn't nearly as long as his - he has very high pitched roof w/no upstairs).

We have confirmed this is NOT the roof leaking. This is not rain coming back in from the flap thing (sorry, I'm not an HVAC lady :-). This is condensation.

So question to you Professionals please, please - How to most other new homes deal with this??? To me, wrapping the ducts with that fat pink insulation (the stuff with a silver skin on one side) would solve - but would it?
The fan seems strong, which I thought was good. Is that an issue??

The builder (punchlist after 3 years, does that give you any clue??) had the idea to rerun and incorporate a bend into the neighbor's duct, forcing a 'trap', and putting some type of tubular water collected there, then let the water run somehow to outside. (sorry, this sounds ludicrous to me).

What is Normal please? Thanks TONS for your ideas or known resolution, or sharing your Standards with us. This is crazy.......

Thanks & Regards - Les.

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